lkml.org 
[lkml]   [2023]   [Oct]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 1/2] arm64: smp: Fix pseudo NMI issues w/ broken Mediatek FW
    On Wed, Oct 04, 2023 at 07:04:12AM -0700, Doug Anderson wrote:
    > On Wed, Oct 4, 2023 at 3:15 AM Marc Zyngier <maz@kernel.org> wrote:
    > >
    > > On Wed, 04 Oct 2023 10:59:50 +0100,
    > > Mark Rutland <mark.rutland@arm.com> wrote:
    > > >
    > > > Given you haven't seen any issues, I suspect those are getting reset to fixed
    > > > values that happens to work out for us, but it is a bit worrisome more
    > > > generally (e.g. the LPI case above).
    > >
    > > It is likely that these SoCs don't even have an ITS.
    >
    > Right. That was what we decided [1] when Marc pointed this out earlier.
    >
    > Overall: we know that this firmware behavior is not good but we're
    > stuck with it. :( At the very least, any new devices coming out will
    > have this fixed. Presumably if old devices are working OK enough today
    > (as long as you don't enable pseudo-NMI) then they can be made to keep
    > working?
    >
    > So circling back: what patch should we actually land?

    For now I'd prefer we took the patch I sent in:

    https://lore.kernel.org/linux-arm-kernel/ZRr8r7XMoyDKaitd@FVFF77S0Q05N.cambridge.arm.com/

    ... as that leaves us no worse than before this series, and it's pretty simple.

    > As of right now only pseudo-NMI is broken, but it would be good to make sure
    > that if the kernel later adds other features that would be broken on this
    > hardware that it gets handled properly...

    Going further than the above, I think there are three options here:

    1) Complete fix: depend on a working firmware, and throw this workaround away.

    IIUC from the above, that's not something you can commit to.

    2) Partial fix: have the kernel save/restore everything.

    IIUC this is unpalatable.

    3) Partial fix: make the ARM64_HAS_GIC_PRIO_MASKING cpucap depend on the
    absence of a "mediatek,broken-save-restore-fw" property in the DT. I believe
    we can check that in early_enable_pseudo_nmi() or can_use_gic_priorities().

    That'll avoid potential issues if/when we change the priorities used for
    pNMI (which is something I've been looking at).

    I'm happy with (3) if Marc is.

    Mark.

    \
     
     \ /
      Last update: 2023-10-05 16:43    [W:5.194 / U:1.176 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site